The Reader and Protagonist Definitely Have to Be in True Love - Chapter 2.2 - Author: … Understood.

It was the turn of the 20th century, and in the Philippine Islands, the fledgling Philippine Republic waited to be crushed by the overwhelming superiority of the American colonial forces.But John McClain, a U.S. Army veteran of the Korean and Vietnam Wars, dies and finds himself in the body of the governor of a remote Philippine province in the year 1898. Initially reluctant to take up arms against his former country and skeptical of the chances of success, he eventually decides to fight for the Republic.Now living his second life as Martín Lardizábal, politico-military governor of Marinduque and armed with modern military knowledge, he will change the course of the Philippine-American War.

When he wakes up, Su Changkong has traveled to a world where troops are chaotic and demons are rampant, and his martial arts qualifications are mediocre, but Su Changkong found that as long as his [lifespan] increases, his talent and potential can be [infinitely] improved!

Wu Qin Xi: imitating tigers, deer, bears, apes, birds and other animals.

Turtle Breath True Dinggong: Imitation Qigong, like a thousand-year-old tortoise breathing, breathing, breathing and closing for a long time, prolonging life!

Celestial silkworm magic: nine transformations of the silkworm, breaking the cocoon into a butterfly, rejuvenating the old and rejuvenating, opening the door of life and death, every transformation is a rebirth!

Cultivation of health boxing, practice the Qi of longevity! There are many corpses on the road of longevity, and Su Changkong has embarked on a longevity martial arts where heaven and earth are destroyed but I am immortal!

- Description from novelbuddy

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

This is a story that follows the courtship between a stone from Hell and a god from Heaven that begins in the underworld and spans for three lifetimes in the mortal realm.